Internal combustion engine ignition device

ABSTRACT

An ignition device for an internal combustion engine comprising a smal pre-chamber 1 having a volume of about 0.7 of the volume of an associated combustion chamber, a small outlet orifice 1a in a pre-chamber having a dimensionaless throat parameter of about 0.4 to 0.7, a valve 2 controlling the introduction of hydrogen gas to the pre-chamber 1 via a valve driver 3 and a spark plug 4 for igniting the hydrogen rich mixture (about 3 times stoiciometric) in the pre-chamber to cause an ignition jet of burning gas to issue from the orifice 1a to promote efficient combustion and to reduce NOx emissions at lean burning mixtures and at higher compression ratios without knock.

REFERENCE TO CO-PENDING APPLICATION

This is a continuation-in-part Application of InternationalPCT/AU92/00552, filed 14 Oct. 1992, for INTERNAL COMBUSTION ENGINEIGNITION DEVICE, which Application designated the United States, and isnow abandoned.

REFERENCE TO CO-PENDING APPLICATION

This is a continuation-in-part Application of InternationalPCT/AU92/00552, filed 14 Oct. 1992, for INTERNAL COMBUSTION ENGINEIGNITION DEVICE, which Application designated the United States, and isnow abandoned.

FIELD OF THE INVENTION

This invention relates to ignition devices for internal combustionengines, and more particularly hydrogen assisted jet ignition (HAJI)devices for improving combustion efficiency. In the presentspecification, the term "hydrogen" is intended to include hydrogen andother fast-burning fuels.

BACKGROUND OF THE INVENTION

Simultaneous control of exhaust emissions and thermal efficiency is anestablished goal in engine design. Optimization of engine design islimited by Cycle by Cycle Variability (CBCV), especially for sparkignition engines. CBCV is observed as either variations in the pressurediagram or as variations in flame propagation between consecutive enginecycles. In the vehicle the consequent unsteadiness in delivered enginepower results in uneven vehicle progress which has been termed surge.Combustion variations require compromises in engine design, the settingof mixture composition and spark timing. This reduces engine power andefficiency at full load in order to meet roughness, noise, and octanerequirements and at part load and idle reduces fuel economy andincreases exhaust emissions in order to control surge.

If CBCV could be eliminated, the engine would run at its best economysettings and still produce a smooth and steady output. In addition, thefuel octane requirements could be reduced, or the compression ratioraised, with a consequent improvement in efficiency. Further, the leanlimit of engine operation could be extended, resulting in a reduction inexhaust emissions and an improvement in thermal efficiency. It has beenshown that the reduction of CBCV in lean-burn engines, together withcontrol of ignition timing, can reduce NOx emissions and at the sametime improve engine thermal efficiency. Another important benefitarising from control of cycle variations is the reduction in enginesurge and improved vehicle driveability while cruising.

Much research has been conducted on lean-burn engines with the intentionof improving efficiency and reducing emissions. The benefits from thelean combustion approach can be theoretically explained as follows. Theexcess air improves the engine's thermal efficiency by increasing theoverall specific heats+ ratio, by decreasing the energy losses fromdissociation of the combustion products, and by reducing the thermallosses to the engine cooling system. In addition, as the flametemperature drops with decreasing fuel air ratio, the NOx production isexponentialy reduced and the excess air may promote a more completereaction of CO and hydrogen fuel emission from crevices and quenchlayers.

It is concluded that at the present state of development, U.S. emissionstandards present a considerable challenge to the realization of thefuel economy advantages theoretically inherent in lean burn engines. Onthe other hand, even though the incentives for lean burn application toautomotive engines are valid and have good theoretical foundation, itsimplementation is a complex problem that requires several conflictingrequirements to be satisfied simultaneously. Lean burn operationincreases the CBCV and deteriorates vehicle driveability. CBCV increaseswith increasing air-fuel ratio.

Many attempts have been made to improve combustion efficiency. Suchattempts include fuel stratification with a rich mixture in the sparkplug region, divided or pre-chamber engines alone or in combination withstratification, and hydrogen enrichment of the whole fuel charge. Noneof these attempts have been entirely successful and the problemsreferred to above remain in evidence.

In the case of non-fuelled divided chamber engines, including the Boschspark plug patented around 1978, the size (volume, connecting passagelength and aperture) of the pre-chamber can only improve combustion at aparticular power output. Thus, while combustion efficiency can beimproved at a given power output, energy tends to be lost at full powerto the pre-chamber walls and other parts of the main chamber by theimpinging jet so that the peak power was reduced by about 10%.Furthermore, since the pre-chamber in the prior art arrangements isunfuelled, relying on the transfer of a fuel mixture from the mainchamber, starting in cold conditions can be difficult.

In a paper entitled "High Chemical activity of incomplete combustionproducts and a method of pre-chamber torch ignition for avalancheactivation of combustion in internal combustion engines" by L. A. Gussakof the Institute of Chemical Physics Academy of Sciences of the USSR,Moscow. (Publication No. 750890 of Society of Automotive Engineers USA)the author discusses the effects of pre-chamber torch ignition on theflame front of a hydrocarbon-air mixture and concludes that optimizationis achieved by employing a pre-chamber volume of two to three percent ofthe compressed combustion chamber volume. While this paper contains somescientific consideration of the combustion products resulting frompre-chamber combustion of a very rich air-hydrogen mixture, the authordoes not come to any conclusion concerning the likelihood of pre-chambercombustion providing a significant benefit in the improvement of enginethermal efficiency while at the same time reducing NOx emissions.

The Patent literature also contains some reference to the burning ofhydrogen in pre-chambers, the most pertinent prior art being U.S. Pat.No. 4,140,090 Lindburg and U.S. Pat. No. 4,760,820 Tozzi. The Lindburgreference provides a small pre-chamber for burning hydrogen butspecifically teaches the introduction of an oxidant to be mixed with thehydrogen fuel to ensure stoiciometric proportions. The reference is alsosilent at the nature of the exit passage. The present applicant hasfound that the mixture in the pre-chamber should preferably be hydrogenrich and the outlet orifice should be carefully dimensioned to ensurethat a proper ignition jet stream issues from the orifice to ensurecomplete combustion of a lean fuel mixture in the combustion chamber.

In the case of the Tozzi reference, the magnetic field generating meansintroduces undesirable complexity and increased power consumption togenerate plasma temperatures of around 4,000° to 6,000° C. Plasmaigniters of the type described by Tozzi have not employed commercialsuccess presumably due to the complexity and power consumptiondifficulties involved.

SUMMARY OF THE INVENTION AND OBJECT

It is an object of the present invention to provide an ignition deviceby means of which combustion efficiency is improved and the problemsoutlined above are at least ameliorated.

The invention provides an ignition device for an internal combustionengine having combustion chamber(s), comprising a small pre-chamberhaving a volume substantially falling within the range of 0.5% to lessthan 2% of the combustion chamber volume, said pre-chamber being closedto the combustion chamber except for one or more small outlet orifices,means for creating a rapidly combustible mixture in said pre-chamber,means for igniting the combustible mixture in the pre-chamber, saidpre-chamber and said orifice(s) being dimensioned to thereby cause anignition jet of burning gas to issue from said orifice in a manner whichpromotes efficient combustion within the combustion chamber(s) internalcombustion engine.

The outlet orifice(s) and the pre-chamber are preferably dimensioned toprovide a dimensionless throat parameter number β= ##EQU1##substantially falling within the range 0.3 to 0.8, and preferably withinthe range about 0.4 to 0.7, and most preferably about 0.4 to 0.6.

By the use of the above ignition device, and particularly by selectionof the dimensionless throat parameter β within the above range, idlecombustion variability is nearly eliminated, even at lean burnoperation. At the same time, low levels of emissions are obtained andunthrottled operation is possible with some sacrifice in efficiency, butwith near zero NOx emissions.

The volume of the pre-chamber is preferably as small as is practicallypossible, the lower limit of the chamber volume being dictated largelyby the ability to physically form the pre-chamber. Pre-chamber volumesof about 0.5% have been achieved with difficulty, while pre-chambervolumes of about 0.7% have been readily achieved and offer the advantageof being capable of location within the diameter of a standard sparkplug connecting portion.

While the availability of hydrogen as a fuel source for combustionwithin a pre-chamber is known from the Gussak paper referred to aboveand from other sources, the ability to significantly reduce the size ofthe pre-chamber as defined above has not been recognized before thepresent invention. Of course, the ability to reduce the size of thepre-chamber not only enables the pre-chamber to be incorporated into amodified spark plug having standard attachment dimensions, but alsosignificantly reduces the total heat losses during the combustionprocess thereby resulting in surprising improvements in lean mixturecombustion and consequential reductions in NOx emissions. Until thepresent invention, it was always expected that a pre-chamber volume atleast as large as that stated by Gussak to provide optimization ofpre-chamber combustion would be necessary to form the necessary torchignition to achieve the expected benefit from this process. It wassurprisingly determined that significantly smaller volumes could be usedwithout compromising the effectiveness of the ignition jet of burninggas produced from the pre-chamber combustion process. It has also beensurprisingly determined that by selecting an orifice throat size βbetween about 0.3 and 0.8 engine efficiency is maximised for leanburning mixtures.

The large surface area to volume ratio of the pre-chamber ensures thatthe residual gas in the pre-chamber is at low temperature, a requirementfor low NOx emission from this region as the gas expands into the mainchamber during expansion. The jet of combustion products, at sonic ornear sonic velocity from the small volume of the prechamber, into themain chamber hydrocarbon fuel initiates a distributed reaction in anultra lean mixture, which can be much leaner than the normal leanflammabilty limit. The distributed reaction is triggered by the presenceof chemically active species in the jet and allows nearly spatiallyhomogeneous burning with excellent repeatability and hence close tospatially uniform temperatures. Along with the ability to use ultra leanmixture this process avoids the higher temperatures found in the regionof the first burned gas in the spark ignition engine in the region ofthe spark plug or in the richer mixture around the fuel jet in thediesel engine which are the source of high NOx emissions.

A preferred fast burning fuel is hydrogen which may be introduced to thepre-chamber from a suitable source or may be produced in-situ within thepre-chamber by catalysis. The amount of hydrogen introduced may bevaried, and may be as low as 0.2% of the fuel charged to the engine. Thehydrogen/air mixture in the pre-chamber is preferably greater thanstoiciometric and may be from about 1.2 to 7 times stoiciometric orhigher, without about 3 times being an effective median value.

The ten times faster flame speed of hydrogen compared with hydro-carbonfuels substantially reduces the variation in the time for ignitionkernel growth, thus virtually eliminating CBCV in combustion under idleand light load conditions. This permits the burning of lean mixtures inthe main chamber; the mixtures may be so lean that throttling may beeliminated whereby thermal efficiency increases and NOx emissionsreduced by as much as three orders of magnitude.

The pre-chamber may be formed as part of a replacement spark plug, ormay be formed as part of the cylinder head in the region of the sparkplug receiving opening. The means for igniting the combustible mixturemay comprise a miniature spark plug, or some other form of sparkgenerating means formed integrally with the means for introducinghydrogen or other rapidly combustible gas into the pre-chamber.

The invention also provides a method of operating an internal combustionengine having combustion chamber(s) comprising the steps of introducinga rapidly combustible mixture into a pre-chamber associated with eachcombustion chamber of the combustion engine and having a volumesubstantially falling within the range 0.5% to less than 2% of thecombustion chamber volume, igniting the mixture in the pre-chamber tocreate a burning fuel ignition jet from one or more exit orifices of thepre-chamber, said jet being controlled to promote efficient combustionwithin the combustion chamber of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood severalembodiments of the invention will now described with reference to theaccompanying drawings in which:

FIG. 1 shows schematically an ignition device according to a firstembodiment of the invention;

FIG. 2 schematically shows an ignition device according to a secondembodiment of the invention;

FIG. 3 schematically shows a third embodiment of the invention;

FIG. 3a is a graph showing changes in indicated thermal efficiency withvarious values of the dimensionless throat parameter β.

FIG. 4 is a sectional elevation of an ignition device according to atest prototype, and

FIG. 5 is a graph showing the variation on specific HC, CO and NOxemissions with variations of specific work with hydrogen at about 0.8%methanol by mass, injected at 90° crank angle BTDC at γ=9;

FIG. 5A is a graph showing variations in NOx emissions with engine poweras work/cycle for normal ignition and for the case of the invention,

FIG. 6 is a graph showing the variation of HC, CO and NOx emissions withpre-chamber H2 injection timing at optimum efficiency mixture of λ=2.1,1.98 and 1.6 at full, half and quarter throttle respectively;

FIG. 7 is a graph showing the effect of the amount of pre-chamber H2injection on efficiency and spark advance at the same optimum efficiencymixtures and throttle settings referred to in relation to FIG. 6;

FIG. 8 is a graph showing the variation of COV of specific work percycle with amount of pre-chamber H2 injection at the same optimumefficiency mixtures and throttle settings;

FIG. 9 is a graph showing the variation of COV of peak pressure withamount of pre-chamber H2 injection at the same optimum efficiencymixtures and throttle settings;

FIG. 10 is a graph showing the effect of increasing compression ratio onindicated thermal efficiency for standard ignition and hydrogen assistedjet ignition, and

FIG. 11 is a graph showing indicated changes in indicated thermalefficiency with engine power as work/cycle for normal ignition, and forthe invention with increased compression ratio.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hydrogen or reformed fuel containing a high proportion of hydrogen ismade in or introduced into a pre-chamber of a volume so small that itmay be formed in the spark plug. Examples of possible designconfigurations are shown in FIGS. 1 to 3.

FIG. 1 shows the arrangement whereby the hydrogen gas is introduced intoa pre-chamber 1 having an outlet orifice 1a by a small value 2 operatedby a valve driver 3 and the mixture ignited by a miniature spark plug 4.Low pressure delivery (about four atmospheres) of hydrogen is used ineach of the embodiments of FIGS. 1, 3 and 4, so that the pressure ofhydrogen delivery is not greater than the fuel supply pressure to thecombustion chamber.

FIG. 2 shows an arrangement in which the spark pug central electrode isconstituted by the hydrogen admission valve 5 which defines a spark gapwithin the gas inlet 6 when the valve is open one unit serving bothfunctions. In this case the hydrogen may be supplied from storagevessels or by the reformation of small amounts of fuel outside thepre-chamber. The hydrogen may be contaminated by the products ofreformation.

FIG. 3 shows a schematic of the pre-chamber in which the hydrogen isgenerated by a reforming catalyst 7, the rate of reformation and thusthe amount of hydrogen produced being controlled by the catalyst bedtemperature, which here is illustrated by means of electrical heatingmeans 8 under control of an engine management computer (not shown). Inthis case, if the amount of fuel within each cylinder is insufficient toproduce a greater than stoiciometric hydrogen mixture, and theeffectiveness of the hydrogen assisted jet ignition system is reducedthereby, additional hydrocarbon fuel may be introduced into thepre-chamber to form a hydrogen-rich mixture, or small amounts ofhydrogen can be directly injected to supplement the hydrogen produced bycatalysis.

The invention is applicable to both four and two-stroke engines.

The amount of hydrogen introduced or reformed fuel produced by catalysismay be varied but small amounts of the order of 0.5 to 2% by mass havebeen found to produce acceptable results. The mixture in the pre-chambershould be greater than stoichiometric and from 1.2 to 7 timesstoiciometric or higher is acceptable, with 3 times constituting areasonable median value. The ten times faster flame speed of hydrogencompared with hydrocarbon fuels substantially reduces the variation inthe time for ignition kernel grown and thus virtually eliminatescycle-by-cycle variation in combustion under idle and light loadconditions. The exodus of the partially combusted hydrogen andhydrocarbon fuel in the pre-chamber provides a jet of enthalpy andreacting products which cause the fuel-lean main chamber products toburn at much lower temperatures and stoichiometry than is possible witha localized ignition source.

The burning of a lean mixture in the main chamber may be sufficientlylean that throttling may be eliminated and thus thermal efficiencyincreased by eliminating pumping work and nitrogen oxide emissionsreduced by as much as two orders of magnitude by the more uniform lowtemperature combustion.

Further, because combustion of the mixtures needed for maximum power isso fast the onset of knock is delayed and compression ratios may beincreased, thus increasing both power output and efficiency.

The volume of the pre-chamber will be less than 2% of the maincombustion chamber clearance volume, and may be as low as 0.5%. This issignificantly smaller than prior art pre-chambers, e.g. VW, at 17% andGussak at 2 to 3%. The number of pre-chamber orifices 1a, orifice throatshape and their direction with respect to the main chamber may be variedand optimized for a particular engine configuration. These parametersare chosen to ensure that the ignition jet or jets issuing from theorifice(s) penetrate the combustion chamber of the engine to such anextent as to maximize efficient combustion. Sharp edges should beavoided when forming the orifice 1a. By correctly choosing the aboveparameters, the ignition jet penetrates to a position approximatelycoincident with the centre of the cylinder, and ignition is then foundto be extremely regular. To ensure a jet ignition gas stream isachieved, the orifice should have a dimensionaless throat parameter β=##EQU2## falling within the range about 0.3 to 0.8.

In this regard reference is made to FIG. 3a, which details test resultsof various pre-chamber orifices, described by the dimensionless throatparameter β "beta". The engine on which the tests were carried out wasthe Wakesha Cooperative Fuel Research Engine (CFR) used for octanerating petrols. The engine was operated at 600 rev/min, the speed usedfor the research octane number determination. Ignition timing was set atthe minimum advance for best torque (MPT) in all cases, the compressionratio was at 9:1 and the fuel supplied to the main chamber was petrol.All tests were at wide open throttle (WOT). The relative air/fuel ratio(to a base of the stoichiometric air/fuel) "lambada", sometimes known asthe excess air fuel ratio, and is the abscissa for the graphs. Theindicated thermal efficiency, the ordinate of the graphs, is absedon thenet (lower) heating value of the fuel. It is clean from the results thatthe throat size "beta" should preferably be in the range of about 0.4 to0.7 for optimum thermal efficiency, although the range 0.3 to 0.8provides acceptable efficiency.

FIG. 4 shows an experimental ignition device embodying the inventionwhich has been subjected to testing using a high speed, single cylinderCFR engine burning methanol fuel. The ignition device comprises a body10 having a cylindrical portion 11 within which a throat insert 12having an outlet orifice 13 of about 1.5 mm diameter received to definea pre-chamber 14 having a volume of about 0.7 cc. This yields a throatparameter β of about 0.4. The cylindrical portion 11 threadably engagesan adaptor 15 which in turn threadably engages the spark plug opening 16in the cylinder head 17 of the engine. Gaskets 18, 19 and 20 arepositioned to seal the adaptor 16 to the cylinder head 17 and the body10 to the adaptor 16, while the gasket 20 seals a hydrogen gas injector21 in an injector opening 22 formed in the body 10. A spark plugreceiving opening 23 in the body 10 receives a spark plug 24, theelectrodes of which project into the pre-chamber 14.

If desired, the pre-chamber may be formed within the cylinder or as anattachment to the cylinder, although these options are less attractivethan forming the pre-chamber in a spark plug body.

The tests conducted using the above described prototype, referred to inthe following description as the hydrogen assisted jet ignition (HAJI)system, relate to an engine speed of 600 r/min for two reasons: first,it is at low speed, low loads that combustion variability is mostnoticeable as engine surge under load or vibration at idle; second, thisis the speed for research octane number (RON) measurement. Thus, theeffects of the ignition system on the octane requirement, or morespecifically, the highest usable compression ratio as a surrogate foroctane number, may be identified.

A wide range of parameters may be employed to describe variability inengine combustion. These may be related to the cylinder pressure, p, themagnitude or the phasing of pressure characteristics such as peak p ormaximum value of dp/dt or the cycle integral value of pressure (w_(c)).Two measures are used here: the coefficient of variation in peakcylinder pressure, COVp (standard deviaton/mean) and the coefficient ofvariation of the indicated specific work (or i.m.e.p.) per cycle,COVw_(c). Fluctuations in the former influence the maximum structuralreactive forces and peak cycle temperatures and in the latter,variability in the indicated thermal efficiency η. The indicated valueof w_(c) is selected rather than the brake value, as the mechanicalefficiency of the `high speed` CFR engine is unusually low because ofits balancing pistons and belt drive arrangement. Emissions of HC, COand NOx are also presented on an indicated specific basis i.e. g/MJ.

The experimental data space has been limited in this presentation to:main chamber mixture composition expressed as λ, the relative air/fuelratio; three manifold air pressures, 95, 73 and 0 kPa, described asfull, half and a quarter throttle, respectively; hydrogen injectiontiming, θ_(H2) ; hydrogen injection quantity expressed as a proportionof the fuel mass supplied, M_(H2) and compression ratio, r. The sparktiming θ_(ign) was always adjusted for the minimum advance of besttorque (MBT); and the main chamber injection timing was at maximum inletvalue lift (98°ATDC) for optimum efficiency in the CFR engine.

The effect of changing the main chamber fuel composition for the rangeof λ=1 to 3.5 for full throttle and smaller range at part throttle wasstudied. Even at full throttle it was possible to reduce the work percycle w_(c) (and the torque) to no load quantities by increasing therelative air/fuel ratio, whereas the lean limit for this engine withnormal ignition is shown to occur at λ=1.64, there exists no lean limitwith hydrogen assisted jet ignition, HAJI, within the usable range ofw_(c). However, it was observed that there is some advantage inthrottling the engine as at the smallest values of w_(c) thermalefficiency, η is higher at a quarter throttle. The peak thermalefficiency η is about two percentage points higher with HAJI over thestandard system.

The range of ignition timing needed for operation from full to no load(w_(c) -820 to 18 kJ/m³) was found to be small and retarded comparedwith conventional ignition. At full load θ_(ign) is after TDC. For alloperating conditions as seen in the COVp was found to be very low andrising only slightly at the lowest values of w_(c) at full and halfthrottles. Usually under light load, this engine has a COVp of about 0.2with the standard ignition system. Whilst these exists substantiallyregular burning to peak pressure, the COVw_(c) variations in the laterburning phases of mixtures leaner than those for maximum η areobservable. The failure to burn all of the main chamber fuel, at leastin some cycles, is evidenced by an upturn in specific HC and CO emissionat full and half throttle as observed in FIG. 5.

The benefits from leaner operation, well beyond the standard engine'slean limit, is evidenced in FIG. 5 where a substantial range ofoperation at specific NOx values of 0.03 g/MJ or much less than onehundredth of the peak NOx. Under these conditions the exhaust NOxconcentrations are less than 1 ppm. The variation in NOx emissions withengine power from the invention and for standard combustion isillustrated in FIG. 5A.

At full throttle these low values of NOx are obtained at w_(c) less than600 kJ/m³ (i.e. for values of torque less than 70% of the maximum) apoint at which the HC and CO are comparatively low and the η for w_(c)=530 kJ/m³, λ=2.15 is a maximum of 40%. Maximum efficiency at half andquarter throttles also correspond with very low NOx values and theadvantage of throttling lies in avoiding the falling efficiency at fullthrottle when λ>3 and the reduced exhaust HC and CO under light load(w_(c)) conditions.

Very small quantities of hydrogen were injected into the pre-chamber toobtain the very low NOx and high η demonstrated in FIG. 5. Thesensitivity to pre-chamber H₂ injection timing (influencing mixing time)and quantity (influencing stoichiometry) have been investigated.

The sensitivity of the engine's performance to H₂ injection timing forthe mixture corresponding to maximum efficiency at each throttleposition was also considered and it was found that η is independent oftiming at full throttle but there is a small advantage (an increase of2% in η) at part throttle by using about 100° BTDC injection timing.More advanced injection requires slightly more advanced spark timing(but very much less than that of the standard engine which is 38° BTDCat a quarter throttle, for example). The combustion variability asCOVw_(c) varies slightly with injection timing, but at advanced timingand half throttle, COVw_(c) is nearly twice tat at full throttle. Thistrend is even more evident in COVp where minima occur close to thetiming of 100°BTDC. There is a trend also for both HC and CO emissions(FIG. 6) to minimise with increasing CO and HC.

The effects of changing the pre-chamber H₂ quantity are demonstrated inFIGS. 7 to 10. In FIG. 7 there is a tendency for η to increase slightlywith reducing quantities of injected H₂. The ignition timing (FIG. 7),COVw_(c) (FIG. 8) and COVp (FIG. 9) indicate that for each throttleopening a point is reached at which combustion variability increases andmore advance is needed to compensate. This is consistent with previousfindings using conditional sampling of the exhaust from fast and slowburn cycles. Corresponding with the increases in variability areincreases in HC and some increase in CO emissions.

A further benefit from the changed ignition system is the increase inhighest usable compression ratio, HUCR. In FIG. 10 the thermalefficiency η for the standard ignition system is shown at maximumefficiency (λ=1.23) and maximum power (λ=0.98) mixtures, and thecorresponding values (λ=2.15) and (λ=0.98) with the HAJI system. Inaddition the value of η at `old max effy`λ=1.23 with the HAJI system isalso included for comparison at equal λ.

With standard ignition, peak efficiency at maximum power mixture, λ=0.90occurs at r=9. At r=10, η falls because knock is encountered. The HAJIsystem at r=9, and with λ=1.23, the optimum for maximum η with standardignition, shows nearly 2% absolute (or 5% relative) increase in η. Thisincrease is considered to be a consequence of the faster burn rate andthe improved combustion variability reducing the overall consequences ofthe combustion time loss. Further increase in λ to increase efficiency(to λ=2.16) is possible and allows an increase of nearly 2% more in η.Moreover, because of the reduced variability and faster burn times FIG.10 shows that r can be increased to 11. At r=12, knock is encountered atmaximum power mixture. At r=11 and λ-2.16, there is a further increasein η of 3%. The total improvement in maximum efficiency of just over 6%absolute represents a relative increase of 15% in η. The improvement inengine power achieved by the invention with increased compression ratiois illustrated in FIG. 11.

The indication that the HAJI can support conventionally port-injecteds.i. engine combustion at mixtures leaner than those reported in theliterature is exemplified at 1200 rev/min engine speed, where COVp ofless than 0.05 can be sustained at λ=4.5. The quantity of hydrogenneeded to sustain such operation is about one tenth that which would beneeded if added homogeneously mixed with the fuel. These is someevidence of increased variability which might be associated with partialburns in the ultra lean mixtures as the COVw_(c) increases to valuesassociated with standard ignition. However, the increases in IIC and COemission under the full and half throttle conditions are attributed tothe thickening of the wall quench layers and reduced oxidation of thehydrocarbons in the substantial crevices of the CFR engine piston. Thebenefit from throttling in reducing the IIC and CO is the result of theincreased fraction of hot residuals in the charge, increasing the cycletemperatures as evidenced by the twofold increase in NOx from 0.6 to 1.2ppm as the throttle is reduced from full to one quarter.

The reason for the optimum H₂ injection timing occurring quite late inthe compression process (i.e. at 100° BTDC) is, with earlier injection,that the lower cylinder pressure allow hydrogen to flow into the mainchamber. It is important to note that if there is no outflow ofhydrogen, the pre-chamber will be fuel rich for all the reported valuesof injected H₂. The increase in COVp (FIG. 9) at low H₂ values may bethe result of injector variability as it approached its minimum opentime of 2 ms. The extremely wide rich flammability limits of hydrogenappear to render the process moderately insensitive to the amount ofinjected H₂.

Our test results showed that MBT spark timing was after TDC for maximumpower mixture. This is an unexpected result because, as the burn rateapproaches that of the Otto cycle's constant volume combustion, equaldistribution of the burn process around TDC would be expected tomaximize the cycle work.

The above demonstration of the CFR engine, working at up to 70% maximumtorque with NOx emission close to ambient levels, is most encouragingfinding as extrapolation of these research engine data to automobileapplication would remove the requirement for stoichiometric operationneeded for the `3-way` catalyst. The hydrogen assisted jet ignition usedto achieve this also confers extremely stable combustion with COV's ofthe peak cylinder pressure and specific work per engine cycle reduced by50 to 80% of that normally achieved with this engine, allowing increasedthermal efficiency at ultra lean operation, at relative air/fuel ratiosof about 2, and about two numbers increase in the highest usefulcompression ratio. The result is an improvement in maximum indicatedthermal efficiency of about 15% simultaneously with the low NOxemissions. The hydrocarbon emissions remain high and if realized inautomotive engines would require after engine clean up.

Near elimination of idle combustion variability by our novel form of"jet" ignition using a small amount of hydrogen addition has beenachieved. At the same time low levels of emissions have also beenobserved. Idle stability will improve vehicle driveability whilstcruising at low engine speeds and high gears when the engine operatesnear idle speed. In addition reduced emissions will be obtained duringvehicle deceleration.

The following conclusions can be drawn from our results:

1. In a conventional ignition system, the cycle-by-cycle variability(CBCV) is initiated in the growth of the ignition kernel, subsequent tospark, during the period when the flame kernel grows to about the scaleof the largest eddies. Three classifications of flame kernels were made,namely (a) stationary kernels, (b) translating kernels and (c) splittingkernels. Subsequent slow burning with stationary kernels has been seenwhile other types of kernels subsequently have fast burning.

2. A novel way of controlling combustion variability for a large rangeof equivalence ratios in the S.I. engine has been obtained with jetignition using small amounts of hydrogen addition. At the same timeimprovement in efficiency and significant reduction in emissions areobtained. A major outcome is that CBCV is not increased with leanmixtures, which is different from that occurring in the conventionallyignited S.I. engine.

3. Unthrottled operation of the S.I. engine with near elimination of NOxemission is possible with this novel method at some sacrifice inefficiency.

4. Idle combustion variations have been nearly eliminated together withlow level of emissions.

I claim:
 1. An ignition device for association with an internalcombustion engine having a combustion chamber of predetermined clearancevolume, comprising a small pre-chamber having a volume of 0.5 or lessthan 2% of the clearance volume, said pre-chamber having at least oneoutlet orifice opening into the combustion chamber, means for creating arapidly combustible hydrogen-rich mixture of about 1.2 to 7 timesstoichiometric in said pre-chamber, and means for igniting thecombustible mixture in the pre-chamber,said pre-chamber and said atleast one orifice being dimensioned to have a dimensionless throatparameter β= ##EQU3## within the range of 0.3 to 0.8, thereby causing anignition jet to issue from said at least one orifice into the combustionchamber so as to promote efficient combustion within the internalcombustion engine.
 2. The ignition device of claim 1, wherein the volumeof the pre-chamber is greater than about 0.5% and less than about 0.8%of the volume of the combustion chamber.
 3. The ignition device of claim2, wherein the throat parameter is about 0.4 to 0.7.
 4. The ignitiondevice of claim 1, wherein the hydrogen rich mixture is about 3 timesstoichiometric.
 5. The ignition device of claim 1, wherein thepre-chamber is formed as part of a structure which is adapted to engagea standard spark plug opening of an internal combustion engine.
 6. Theignition device of claim 5, wherein said pre-chamber forms part of aspark plug structure.
 7. The ignition device of claim 1, wherein saidmeans for creating a combustible mixture in said pre-chamber comprisesmeans for injecting rapidly burning fuel into said pre-chamber.
 8. Theignition device of claim 1, wherein said pre-chamber includes areforming catalyst and heating means for generating a rapidly burningmixture within said pre-chamber.
 9. An internal combustion engine havingan ignition device according to claim
 1. 10. A method of operating ainternal combustion engine having a combustion chamber of predeterminedclearance volume, comprising the steps of associating with thecombustion chamber a pre-chamber having a volume of 0.5 to less than 2%of the predetermined volume and comprising at least one orifice openinginto the combustion chamber, introducing into the pre-chamber a rapidlycombustible hydrogen-rich mixture of about 1.2 to 7 timesstoichiometric, and igniting the mixture in the pre-chamber to create aburning fuel ignition jet from said at least one orifice to promoteefficient combustion within the combustion chamber,said pre-chamber andsaid at least one orifice being dimensioned to have a dimensionlessthroat parameter β= ##EQU4## within the range 0.3 to 0.8.
 11. The methodof claim 10, wherein the dimensionless throat parameter is about 0.4 to0.7.
 12. In combination, an internal combustion engine having acombustion chamber of predetermined clearance volume and an ignitiondevice comprising a small pre-chamber having a volume of 0.5 to lessthan 2% of the clearance volume, said pre-chamber having at least oneoutlet orifice opening into the combustion chamber, means for creating arapidly combustible hydrogen-rich mixture of about 1.2 to 7 timesstoichiometric in said pre-chamber, and means for igniting thecombustible mixture in the pre-chamber,said pre-chamber and said atleast one orifice being dimensioned to have a dimensionless throatparameter β= ##EQU5## within the range of 0.3 to 0.8, thereby causing anignition jet to issue from said at least one orifice into saidcombustion chamber so as to promote efficient combustion within theinternal combustion engine.